blue skies or rain tomorrow? Where do clouds come from? Why do we have thunder and lightning? Answer all these questions and more with entertaining experiments geared to youngsters in the second and third grades. Using blown-up balloons and the refrigerator, test the difference between cool and hot air. Wrap a thermometer in a wet paper towel, wait a little bit, and then compare it to one that's left unwrapped: it will reveal the secrets of humidity. (And explain why two days with exactly the same temperature can feel completely different.) Make some morning dew to understand why the grass is wet when you wake up--even if it didn't rain. Create a hailstorm from blueberries, start a mini-tornado, keep a weather diary, and more!

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